1. Field of the Invention
The present invention relates to a videoconferencing system that uses an existing network to allow bidirectional connections to be readily and quickly established among PCs at multiple sites. In particular, the present invention relates to a videoconferencing system on a network that includes dual (multiplexed) operation support servers to improve reliability and enables quick and automatic switching to an operation support server in a standby state if an operation support server in service fails, thereby allowing a video conference to be smoothly continued without interruption with improved usability.
2. Description of the Related Art
As is commonly known, a videoconferencing system allows multiple remote sites to send and receive video and audio to conduct a video conference while viewing the video displayed on monitor screens. Videoconferencing systems widely used today typically use telephone lines. Once a call is established over a telephone line, video and audio can be sent and received and an image is displayed and audio is heard. However, a basic function of communication over a telephone line is one-to-one bidirectional communication. Therefore, conventionally a multipoint communication control unit is interposed and is connected to each site terminal through a telephone line.
As a multipoint communication control unit, there is such a control unit for example as has a function that, by a support of hardware, generates a composite video-audio information by combining pieces of video and audio information individually sent from site terminals at different sites and returns the composite video-audio information to the site terminals to permit each site terminal to display reduced images of the other site terminals (see Japanese Patent Laid-Open No. 7-162823). This function implements a pseudo one-to-many bidirectional communication by using one-to-one bidirectional communication. In addition, the videoconferencing system allows site terminals to basically flexibly participate in and leave a video conference. This is possible because the multipoint communication control unit connects and disconnects a telephone line to allow a site terminal to participate in and leave the conference. However, the videoconferencing system requires high equipment cost. In addition, since the system essentially uses telephone lines, telephone line charges and therefore communication cost increase with the distance between the multipoint communication control unit and the sites. Furthermore, because of a limited bandwidth, the video quality is low and it is difficult to smoothly transmit video and audio.
Therefore, a videoconferencing system has been developed that uses an existing network, instead of telephone lines. In a videoconferencing system using a network, each site terminal does not require high equipment cost because the site terminal requires only a personal computer (PC) including a camera (video input device) and a microphone (audio input device), and also communication cost can be significantly reduced. Moreover, such a system is basically capable of one-to-many bidirectional communication and, thanks to a broad bandwidth, achieves high video quality and smooth transmission of video and audio.
However, there is a problem that each individual site PC that is going to participate in a video conference has to perform operation for connecting to many other site PCs and open a number of viewers required. A user who wants to hold a video conference should provide information such as the start time of the video conference and connection information for site PCs that will participate in the video conference to the site PCs in advance by e-mail or otherwise, and the individual site PCs simultaneously perform operation for connecting to the other site PCs at that start time. The video conference cannot be started until this preparatory operation has been completed. The operation for interconnection between site PCs before starting a video conference is considerably troublesome. There is an upper limit of four sites that can participate in a video conference at a time in the present circumstances. Another problem with such a videoconferencing system is that it is difficult for an additional site to participate in an ongoing video conference or for a site PC participating in a video conference to leave the ongoing video conference. In order for a site PC to participate in or leave an ongoing video conference, the other site PCs have to individually perform operation for connecting to or disconnecting from the site PC that is going to participate in or leave the video conference.
As a technique to solve these problems, the present inventors have proposed in the past a videoconferencing system that uses a network, in which an operation support server on a network includes a site information management function which stores and manages connection information for all site PCs capable of participating in a video conference and a connection support function which generates live camera information for each site that describes a destination to which a connection is to be automatically established and writes the live camera information in a folder for each site in response to a video conference start request and deletes live camera information in response to a conference close request. Each site PC includes a monitor function which periodically accesses a folder for its own site on the operation support server to check to see whether there is live camera information and a connect function which, when there is live camera information, reads the live camera information, enables transmission to each site described in the live camera information and opens as many viewers as the number of the sites to enable reception from the sites, and when live camera information is deleted, stops transmission to the sites and terminates the associated viewers for the sites. Each site PC reads live camera information written by the operation support server in a folder for the site and automatically connects to and disconnects from the other site PCs and automatically opens and closes a viewer to start and close a video conference. (Japanese Patent Application No. 2007-21711).
Since the videoconferencing system described above uses a network, each site terminal may be a simple PC equipped with a camera and a microphone; the system therefore has an advantage in that the equipment cost is low and communication cost can be significantly reduced. In addition, since the system stated above is basically capable of performing one-to-many bidirectional communications and the system's bandwidth is broad, the system has another advantage in that the video quality is high and video and audio can be smoothly transmitted. Furthermore, since what is required of each site PC is simply to monitor the folder of its own use in the operation support server constantly with sending and receiving enabled corresponding to the live camera information described therein and to open a needed number of viewers, interconnection can be automatically established enabling a video conference among multiple sites to be readily and quickly opened and closed even if the number of sites that participate in a video conference increases. Moreover, operation for an additional site PC to participate in an ongoing video conference or for a participant site PC to leave an ongoing video conference (and associated operation for connecting or disconnecting communication and opening or closing a viewer) can be automatically and quickly performed simply by changing live camera information in each site folder on the operation support server. Therefore, the video conference can be smoothly conducted as if participants were in the same room. Thus, the videoconferencing system has considerably advantageous effects as compared with the conventional-art system.
However, the videoconferencing system has room for improvement in terms of the reliability of the system and the stability of communication among others, because the system basically relies on the use of a single operation support server. In this connection, a dual-system of the operation support server is conceivable to improve the reliability. However, providing accessible servers simply in plural can worsen operability and impair inherent advantages of the videoconferencing system if such provision of plural accesses cause a video conference to be interrupted or cause switching from one operation support server to another to require much time and labor.
Objects to be achieved by the present invention are to improve the reliability of a system and ensure the stability of communication by using dual (redundant) operation support servers and to enable a video conference to be smoothly continued without interruption by automatically switching from one operation support server to another, thereby minimizing impediments to the progress of the conference.